Why the potato?

Dead Beat, Chapter 24. Dresden rummages through the Beetle. “Next to a couple of holy water balloons, an old pair of socks and an old heavy potato, I found a crinkling plastic package”. I get the holy water, socks sounds like normal car detritus, but the potato? Why the potato? Why is its heaviness called out? Am I over thinking this? Does Jim keep a potato in his car and somehow think this is normal?